Stainless Steel Heat Transfer Oil Coil Tube — Product Technical Specification
1. Product Overview
The Stainless Steel Heat Transfer Oil Coil Tube is a precision-engineered coiled piping component designed for high-temperature heat transfer oil (HTO) circulation systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube serves as a critical heat exchange element in industrial thermal fluid systems, where it facilitates efficient energy transfer between hot heat transfer oil and process loads under sustained elevated temperatures and pressures.
Coil tubes (also referred to as helical tubes or spiral tubes) are formed by cold-bending seamless stainless steel tubes into continuous helical configurations. The helical geometry provides an exceptionally high surface-area-to-volume ratio, enhancing convective heat transfer coefficients by 30–50% compared to straight tubes of equivalent cross-section. This makes coil tubes indispensable in applications requiring compact heat exchangers operating within the temperature range of 250 °C to 400 °C.
This specification is informed by failure analysis methodologies applied to heat transfer oil coil tubes, incorporating lessons learned from real-world degradation scenarios including thermal fatigue, oxidation scaling, intergranular corrosion, and mechanical over-stress. The design and material selection described herein are optimized to mitigate these known failure modes.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from austenitic stainless steel seamless tubing, with the following grades available:
- SUS304 / AISI 304 (UNS S30400) — General-purpose grade with excellent formability and moderate oxidation resistance up to 870 °C. Suitable for heat transfer oil systems operating below 350 °C.
- SUS316 / AISI 316 (UNS S31600) — Molybdenum-enhanced grade (2.0–3.0% Mo) offering superior resistance to pitting and crevice corrosion. Recommended for systems using synthetic heat transfer oils with chlorinated additives or where sulfur-containing compounds are present.
- SUS321 / AISI 321 (UNS S32100) — Titanium-stabilized grade (0.08–0.25% Ti) providing enhanced resistance to intergranular corrosion at temperatures above 425 °C. Ideal for prolonged high-temperature service.
- SUS310S / AISI 310S (UNS S31008) — High-chromium (24–26% Cr), high-nickel (19–22% Ni) grade with outstanding oxidation and scaling resistance up to 1150 °C. Reserved for extreme thermal cycling applications.
2.2 Mechanical Properties (Cold-Wrought Condition)
| Property | SUS304 | SUS316 | SUS321 | SUS310S |
|---|---|---|---|---|
| Tensile Strength (MPa, min.) | 520 | 520 | 520 | 520 |
| Yield Strength (MPa, min.) | 205 | 205 | 205 | 205 |
| Elongation (% at break, min.) | 40 | 40 | 40 | 40 |
| Hardness (HB, max.) | 217 | 217 | 217 | 217 |
| Density (g/cm³) | 8.00 | 8.03 | 8.00 | 8.03 |
| Thermal Conductivity (W/m·K, at 100 °C) | 16.3 | 14.6 | 16.3 | 24.7 |
| Thermal Expansion Coefficient (×10⁻⁶/K, 100–400 °C) | 16.5 | 16.2 | 16.5 | 17.7 |
2.3 Corrosion Resistance
All listed grades exhibit a passivation oxide layer (Cr₂O₃) that self-heals in the presence of oxygen, providing inherent resistance to atmospheric and aqueous corrosion. The corrosion resistance is particularly critical in heat transfer oil systems where localized overheating (hot spots) can lead to tube wall thinning and eventual rupture. The molybdenum content in SUS316 and titanium stabilization in SUS321 provide additional safeguards against intergranular attack during prolonged exposure to temperatures between 425 °C and 815 °C.
3. Specifications
3.1 Dimensions and Configuration
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 12.7 mm – 57.0 mm (0.5" – 2.0") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 1.0 mm – 4.0 mm (standard); up to 6.0 mm (custom) | ASTM A213 / GB/T 14976 |
| Coil Bending Diameter (Min. Bend Radius) | ≥ 3.0 × OD (cold-bent); ≥ 2.0 × OD (hot-bent) | GB/T 12770 |
| Coil Length (per spool) | 5 m – 50 m (customizable) | — |
| Coil Pitch | 1.2 × OD – 2.5 × OD (typical) | — |
| Number of Turns | 3 – 200+ (per coil assembly) | — |
| Surface Finish | 2B (mill finish); BA (bright annealed); Electropolished (Ra ≤ 0.4 μm) | ASTM A480 |
| End Preparation | Plain ends; Beveled ends (37°); Flanged ends (ASME B16.5) | ASME B16.5 / GB/T 9112 |
| Operating Temperature Range | −196 °C to 870 °C (SUS304/316/321); up to 1150 °C (SUS310S) | — |
| Maximum Operating Pressure | Determined by hoop stress calculation per ASME BPVC Section VIII Div. 1 | ASME BPVC VIII-1 |
| Heat Transfer Oil Compatibility | Mineral-based, synthetic (PAO, silicone, PAB), and organic (diphenyl oxide, terphenyl) HTOs | ASTM D2622 / ASTM D6584 |
| Applicable Standards | ASTM A213, ASTM A312, GB/T 14976, EN 10216-5, JIS G3459 | — |
3.2 Typical Configuration Options
- Single-Helix Coil — A single continuous helical winding; simplest configuration, suitable for moderate heat duty.
- Double-Helix Coil — Two parallel helical windings; doubles the heat transfer area within the same envelope volume.
- Spiral Coil (Archimedean Spiral) — Flat spiral winding in a single plane; used in plate-and-coil heat exchangers.
- Multi-Pass Coil Bundle — Multiple coil tubes arranged in parallel or series within a shell; used in shell-and-coil heat exchangers.
4. Manufacturing Process
4.1 Raw Material Selection and Inspection
Seamless stainless steel tubes are sourced from certified mills meeting ASTM A213 or GB/T 14976 specifications. Incoming material undergoes:
- Chemical Composition Verification — Spectrographic analysis (OES or ICP) to confirm elemental content within specified ranges.
- Mechanical Testing — Tensile and hardness testing per ASTM A370.
- Non-Destructive Examination (NDE) — Eddy current testing (ECT) per ASTM E213 and hydrostatic pressure testing per ASTM A269 to detect internal and external defects.
- Dimensional Inspection — OD, wall thickness, and straightness verification using ultrasonic thickness gauges and optical comparators.
4.2 Coil Bending Forming
The helical coil geometry is achieved through precision cold-bending or hot-bending processes:
- Cold Bending — Utilizes CNC-controlled bending machines with mandrel support to form coils with bend radii ≥ 3.0 × OD. Cold bending introduces work hardening, which increases yield strength by 15–25% but reduces elongation. Suitable for SUS304 and SUS316 grades.
- Hot Bending — The tube is heated to 900–1100 °C (solution annealing temperature) and formed with a minimum bend radius of 2.0 × OD. Hot bending preserves the annealed microstructure and mechanical properties. Required for thicker-wall tubes (≥ 4.0 mm) or SUS321/SUS310S grades where cold workability is limited.
- Post-Forming Annealing — Cold-bent coils are subjected to solution annealing (1010–1120 °C, followed by rapid water quench) to relieve residual stresses and restore full ductility. This step is critical for preventing stress corrosion cracking (SCC) in chloride-containing environments.
4.3 Surface Treatment and Passivation
- Acid Pickling — Immersion in nitric/hydrofluoric acid solution (HNO₃/HF) to remove oxide scale and mill contaminants.
- Passivation — Treatment with nitric acid (20–30% HNO₃) per ASTM A967 or AMS 2700 to enhance the chromium oxide passive film thickness to ≥ 5 nm.
- Electropolishing (optional) — Electrochemical smoothing to achieve surface roughness Ra ≤ 0.4 μm, essential for hygienic or high-flow-velocity applications.
4.4 Final Inspection and Testing
- Dimensional Verification — Full-length measurement of coil diameter, pitch, and total length using coordinate measuring machines (CMM) or laser scanning.
- Pressure Testing — Pneumatic or hydraulic pressure testing at 1.5 × maximum operating pressure per ASME BPVC Section VIII.
- Leak Testing — Helium leak testing (sensitivity ≤ 1×10⁻⁹ Pa·m³/s) for critical applications.
- Visual Inspection — 100% visual examination for surface defects, dents, or deformation at bend points.
- Material Traceability — Heat number marking and documentation for full traceability from mill certificate to final product.
5. Applications
5.1 Primary Application: Heat Transfer Oil Systems
The primary application domain is industrial heat transfer oil (HTO) systems, where coil tubes serve as heating or cooling elements in:
- Petrochemical and Refining — Feed preheating, fractionation column reboilers, and heat recovery systems in crude oil distillation units. Operating temperatures: 300–400 °C.
- Polymer and Chemical Processing — Jacketed reactor heating coils, polymer melt processing equipment, and chemical synthesis reactors requiring precise thermal control.
- Food and Pharmaceutical — Steam and heat transfer oil heating coils in pasteurization, sterilization, and drying equipment (SUS304/316 for sanitary compliance).
- Textile and Rubber Industry — Calender rollers, extruder barrels, and vulcanization presses heated by circulating heat transfer oil.
- Power Generation — Organic Rankine Cycle (ORC) systems and waste heat recovery units using coil heat exchangers.
5.2 Secondary Applications
- Industrial water heating systems (high-temperature hot water, up to 180 °C)
- Waste heat recovery and energy efficiency retrofits
- Process cooling coils in chemical reactors
- Specialty heat exchangers in pharmaceutical and bioprocessing industries
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications:
| Certification | Scope | Relevance |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Ensures consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System | Controls environmental impact of manufacturing processes |
| ISO 45001:2018 | Occupational Health and Safety | Worker safety in manufacturing and handling operations |
| EN 10204 3.1 | Material Test Certificate | Third-party verified material certification for each heat lot |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive | Compliance with EU pressure equipment safety regulations |
| ASME "U" Stamp | Pressure Vessel / Piping Components | Authorization for fabrication of pressure-containing components |
| NORSOK M-650 | Offshore Materials Specification |